This invention relates to an exhaust system for an outboard motor and more particularly to an improved exhaust system that will ensure against water inadvertently being drawn into the engine through its exhaust system.
Conventionally, outboard motors employ exhaust systems that convey the exhaust gases from the engine to an expansion chamber and silencing system positioned in the drive shaft housing through exhaust pipes that depend from the power head into the expansion chamber. The exhaust gases are then discharged to the atmosphere from this expansion chamber through a high speed below the water exhaust gas discharge. In addition, a restricted above the water exhaust gas discharge is provided for the discharge of exhaust gases when the watercraft is relatively stationary and the underwater exhaust gas discharge is so deeply submerged that the low pressure of the exhaust gases cannot exit through this path.
Although this type of system is generally effective, for tuning and silencing purposes, it is necessary for the exhaust pipe or exhaust pipes to depend some distance into the expansion chamber. Normally, these exhaust pipes terminate at an area in the expansion chamber just slightly above the water level therein when the watercraft is stationary. It should be readily apparent that due to the underwater exhaust gas-discharge, water will enter the expansion chamber through the exhaust system.
It is also well known, however, that the exhaust pulses of an engine, particularly a two-cycle engine, tend to have periods when the exhaust pressure is less than atmospheric. Thus, there is a danger that water in the expansion chamber can be drawn into the engine through the exhaust system. Furthermore, there are instances where the water level can be higher than the normal stationary water level. For example, when decelerating abruptly, the water level can rise significantly and this can cause a possibility of water entering the engine through its exhaust system. In addition, when the outboard motor is tilted up to an out of the water position, residual water in the expansion chamber can at times flow back to the exhaust pipes and enter the engine. Of course, none of these effects is desirable.
It is, therefore, a principal object of this invention to provide an improved exhaust system for an outboard motor.
It is another object of this invention to provide an exhaust system for an outboard motor that can in a convenient and simple way ensure against the entry of water into the engine through its exhaust system.
In conjunction with multiple cylinder engines, it is the practice to employ an exhaust manifold for each bank of cylinders and thus a number of exhaust ports discharge into this manifold. Of course, this means that the lowermost cylinders are more prone to receiving water through the exhaust system under the extreme conditions noted above.
It is, therefore, a still further object of this invention to provide an improved exhaust system for a multiple cylinder engine of an outboard motor.